Multi-Stream Transport (MST) is what allows daisy-chaining multiple DisplayPort displays off a single DisplayPort connector. Multi-Stream Transport was added to the DisplayPort 1.2 specification and can be achieved not only by daisy-chaining but also using a MST hub for having up to three connectors off a single DisplayPort connector.
DisplayPort MST is common right now among some 4K DisplayPort monitors that are technically two panels exposed side-by-side. It was also discovered that among newer Lenovo ThinkPad docks they are using one DisplayPort connector and then from the dock exposing VGA, HDMI, DVI, and DisplayPort connections. This is what's led David Airlie at Red Hat to begun hacking on the MST handling for the DRM/KMS drivers.
Right now trying to use MST will just yield a single-stream and the same image being broadcast across all displays. So far David has brought up the first step of encoding the topolgy discovery message and receiving responses from the dock. However, there's much more work ahead. Besides the Lenovo dock, he will also be playing aorund with a DP MST hub for AMD and NVIDIA DRM graphics drivers with the ThinkPad T440s using Intel graphics. More details on this open-source DisplayPort MST work can be found via David's blog. The only downside to this work is that it's taking him away from Virgil3D development.